BT suffers huge broadband failure across much of UK
A "power failure" at a major exchange in Birmingham has seen huge numbers of BT Broadband customers across the UK cut off.
The company said those affected numbered into the hundreds of thousands - about 5% of its total customers.
Business users were particularly badly affected, with many reporting considerable lost revenue as a result.
BT said the service has now been fully restored, advising customers to "turn their hub or modem off and on again".
The first reports of lost connections began to appear at about 13:00 BST.
By 15:00 many customers on consumer packages reported being able to gain access, but business customers had to endure longer delays.
In a statement, the company said: "We can confirm that, as a result of a power failure at one of our major exchanges, some customers may have experienced loss of broadband service for a brief period this afternoon.
"All services have now been restored, with the majority of BT's consumer broadband customers' service being restored within just one hour.
"Some business customers' broadband service may have been affected for a slightly longer period. Should any customers continue to experience difficulty in accessing their broadband service, they are advised to turn their hub or modem off and on again."
Many businesses contacted the BBC to vent their frustration at the service, suggesting today's problems have had a serious impact on sales.
Daniel Morris, in London, said: "Really frustrating for a small business as we are so reliant on the internet.
"Best thing was the BT helpline advising customers to logon to BT.com if they can't get through on the phone - not easy logging in without internet!"
Greg Gillies, director of IT support company Pond Group, added: "We were unable, along with the rest of the country, to get hold of BT for confirmation and had to rely on Twitter for unconfirmed updates."
In response, BT has said they have received a "large number of calls" and was doing its best to answer queries using social media and other methods.
"We have been doing our very best to keep customers informed," the spokesperson added.
"BT apologises for any inconvenience caused."